Space discharge amplifier system



y 23, 1929- A. cs. LANDEEN SPACE DISCHARGE AMPLIFiER SYSTEM Filed Jan. 11, 1926 Patented July 23, less.

ETEEE COMPANY, INCORPORATED, OF NEW YORK, N. L, CORPORATION OF NEW YURK.

SPACE DISCHARGE AMPLIFIER SYSTEM.

Application filed January 11, less.

This invention relates tospace discharge amplifier systems, and more particularly, to,

a method of and means for operating such systems to suppress certain undesired modulation products.

In circuits, including a space discharge device, there are generally present in the output circuit certain modulation products in addition to the waves repeated or detected by the device. Thus, when a single frequency wave is applied to the input circuit, the output circuit will contain a wave of the funda mental frequency and waves of various frequencies harmonically related to the fundamental. If a complex wave, that is one composed of two or more frequencies, is applied to the input circuit the output circuit will contain waves which are harmonically related in frequency to the input waves, and also components having frequencies equal to the sum and difference of the respective fundamental frequencies and various higher order components. Assuming by way of 1llustrat1on that two waves of frequency F and F are applied to the input circuit of a space discharge device, the output circu1t will cont-am components of the following frequencies: F F 21?}, 2F, etc. F F 2F iF F- iQF etc. Of the above mentioned products F and F are commonly called first order modulation products. 211, 2F and f iF, are called second order modulation products. 3F 3E 2F i-F and F QF, may be considered third order modulation products. 7

lnspace discharge detector and modulator systems, the second .or higher order modulation products are desired, while in space discharge amplifier systems for distortionless amplification first order products alone should be present.

In space discharge amplifier systems in general and particularly those which are excited by means of a modulated wave, various higher order modulation products are present in the output circuit in addition to the desired first order products. However, as products of a higher order than the third are usually negligible with respect to third and lower order modulation products, by suppressing currents of the third order in asystem theeffect of all odd order modulation products is practically eliminated.

It is an object of this invention to suppress third order modulation products in a space discharge amplifier system.

Serial 1N0. 80,485.

Another object is to improve the quality and eliminate distortion in carrier transmisslon systems. v

It has been found that in the operation of space discharge amplifier systems, if a certain critical value of load impedance is used, the amplitude of third order modulation products inthe system may be decreased to substantially zero. The above objects and others which will be apparent as the nature of the invention is disclosed are accomplished in a with the accompanying drawing forming a part thereof in which Fig. I illustrates a series of curves to be used inexplanation of the operation of the system, Fig. 2 shows diagrammatically one embodiment of this invention involving a single amplifier tube, and Fig. 3 illustrates a modification thereof involving a pair of amplifier tubes connected in push-pull relationship. 7

Referring to the system disclosed in Fig. 2 there is shown a source 1 of waves which may comprise waves of either high or low. frequencies. This source is connected to the input circuit of space discharge device 2 the output circuit of which is connected to a variable load impedance 3 and a current measuring circuit 1. Resistance 5 is inserted in series with source 1 in the input circuit of space discharge device 2 in order to control the value of the potential impressed on thecontrol electrode of the space discharge device. The space current for device 2 is derived from source 6 through choke coil 7 which is adapted to prevent high frequency currents from passing through the source. Blocking condenser 8 serves to prevent direct current passing through the load impedance 3.

The current analyzing circuit 4 comprises an inductance 9 and a capacity 10 in series with a suitable meter A connected in shunt to resistance 11, the impedance of which is small in comparison to that of load resistance 3.

harmonic of the impressed wave.

I curve a of Fig. 1 in which the amplitudeof the third harmonic due to a simple wave is plotted as a function of the load resistance.

A change in sign of the ordinates of curve a. indicates a change 1n those of the correspondin g currents. For this particular system the value of these products becomes zero at a load resistance slightly below one thousand ohms. Consequently when resistance 3 is adjusted to have this value the amplifier system will be found to be substantially free from third order modulation products. The various higher odd order products are also believed to be reduced in amplitude under the same operating condition but as the effect of these products is comparatively small their suppression is relatively unimportant. Applicant is not aware of the exact scientific explanation and reason for the above disclosed effect but that such is the fact has been determined positively by experimental processes.

It has been found that the characteristics of space discharge devices relative to third order modulation products vary considerably. Therefore, although the thirdorder products cannot generally be suppressed simultaneously inthe two tubes. they may be balanced against each other in a system employing two space discharge devices connected in push-pull relationship. This is shown by referring to Fig. 3 in which modulated waves are impressed upon the input circuits of space discharge devices 12 and 13 by means of transformer 17. Devices 12 and 13 are connected in opposing or push-pull relationship in the usual manner which is well known in the art. The currents in the output circuit of these devices are impressed by means of transformer 14; upon a suitable load or line 15 which represents any type of load circuit that may be employed. The impedance of load 15 is varied by resistance 16 connected in parallel thereto.

In the operation'of the system shown in Fig. 3 devices 12 and 13 are assumed to have operating characteristics such as represented by curves a and b respectively in Fig. 1. The summation of thecurrents represented by these two curves is shown by curve 0 which passes through the zero axis at a load resistance of approximately 1500 ohms indicating that the third order products in the two tubes are of opposite phases. This value of load resistances may be determined indirectly by plotting the characteristics of the two space discharge devices separately in a system similar to that shown in Fig. 2 and determining from the curves obtained the value of the load resistance required to produce third order modulation products of approximately zero amplitude.

By operating the system in the manner above described the distortion of the transmitted wave due to the presence of odd order modulation products is practically eliminated inasmuch as the products causing the greatest distortion, that is, the third order products, are reduced tosubstantially zero amplitude and inasmuch as products of highor odd orders than the third althoughoriginally of comparatively slight importance are still further reduced in amplitude. Inasmuch as a push-pull amplifier tends to suppress all even order modulation products this system will contain substantially no products of higher order than the first.

Although this invention has been shown and described as applied to particular systems it is not to be limited thereto but only in cuit and an output circuit, a source of waves to be amplified associated with said input circuit, and a load associated with said output circuit having its impedance proportioned substantially to the critical value with respect to said discharge device at which value the third-order modulation products impressed on the load are reduced substantially to zero.

2. An amplifier comprising a pair of space discharge devices connected in push-pull relation with respect to an incoming and an outgoing circuit, said devices being balanced to suppress in the outgoing circuit the secondorder modulation products of waves from the incoming circuit, said outgoing circuit having its impedance proportioned to substantially the critical value at which the third-order modulation products from one of said devices neutralize those from the other, whereby said circuit repeats the fundamental frequency of the incoming waves while suppressing in the outgoing circuit both the second-order and the third-order modulation products.

3. In a transmission system, an incoming circuit, an outgoing circuit, and a repeating the voltage for third-order modulation products of waves in the incoming circuit is substantially zero.

4:. In combination, a pair of space discharge devices, each having a cathode, an anode, and a grid or impedance control element, said devices being connected in push pull relation with respect to a source of waves to be repeated and to an outgoing circuit, said devices having substantially similar characteristics with respect to the second-order modulation products appearing in their anode-cathode circuits, whereby said products are suppressed in the outgoing circuit, said outgoing circuit having an impedance of substantially the critical value at which said devices produce third-order modulation prod ucts of the same magnitude but opposite phase whereby the third-order modulation products from said devices are suppressed in said outgoing circuit.

5. An amplifying circuit for producing amplified waves substantially free of all modulation products of higher order than the first, comprising a push-pull circuit balanced to suppress the even-order modulation products and a load circuit presenting an impedance to said push-pull circuit of the critical value at which the odd-order modulation products higher than the first are suppressed, substantially as described.

6. A space discharge amplifier system including a source of modulated waves, a load circuit and a measuring circuit, said measuring circuit being selective of certain third order modulation products and the impedance of said load circuit being such that the amplitude of third order modulation products is substantially Zero.

7. The method of suppressing third order modulation products in an electron discharge 

